Interpretive Summary: Problem: When pesticide resistance genes are inadvertently transferred between closely related weed and crop species due to outcrossing, individuals with weedy traits may be produced. The presence of these plants may have various effects, including altering the way in which the weed population changes over time, the persistence of the transferred resistance genes in farm fields, and various approaches to weed management and containment. We attempted to measure outcrossing from a number of weedy red rice types into rice under field conditions, and to evaluate the appearance seed production of resulting hybrids.
Accomplishment: Hybrids produced from outcrossing between a herbicide-resistant rice variety and red rice grew to heights up to 150 cm, flowered slightly later than the rice parent, and produced up to 50% more seed than the rice parent. Seeds of all hybrids were red and shattered from the plant at maturity. For the majority of hybrids, seed germination was higher than that of the red rice parent. The outcrossing (or gene flowrate) from red rice into rice was 0.01–0.2% and differed by red rice type.
Contribution: This research confirmed that red rice plants can be vectors of gene flow back to cultivated rice within rice fields. Thus, gene flow reduction and management strategies should take this into account for optimum results.

Technical Abstract:
Gene transfer from weeds to crops could produce weedy individuals that might impact upon the evolutionary dynamics of weedy populations, the persistence of escaped genes in agroecosystems and approaches to weed management and containment of transgenic crops. The present aim was to quantify the gene flowrate from weedy red rice to cultivated rice, and evaluate the morphology, phenology and fecundity of resulting hybrids. Field experiments were conducted at Stuttgart
and Rohwer, Arkansas, USA. Twelve red rice accessions and an imazethapyr-resistant rice (Imi-R) were used. Hybrids between Imi-R rice × red rice were 138–150 cm tall and flowered 1–5 days later than the rice parent, regardless of the red rice parent. Hybrids produced 20–50%more seed than the rice parent, but had equivalent seed production to the majority of red rice parents. Seeds of all hybrids were red, pubescent and dehisced at maturity. For the majority of hybrids, seed germination was higher than that of the red rice parent. The gene flowrate from red rice to rice was 0.01–0.2% and differed by red rice biotype. The hybrids had higher fecundity and potential competitive ability than the rice parent, and in some cases also the red rice parent.
Red rice plants are vectors of gene flow back to cultivated rice and other weedy populations. The progeny of red rice hybrids from cultivated rice mother plants have higher chances of persistence than those from red rice mother plants. Gene flowmitigation strategies should consider this scenario.